- To assess the safety of elvucitabine therapy in HIV-1 infected subjects with a documented M184V variant Number of Subjects: 20 Number of Study Centers: Multi-center study Study Population: HIV-1 infected subjects who are presently failing an antiretroviral therapy regimen containing lamivudine or emtricitabine, genotypically demonstrate a MI84V variant, and have an HIV RNA plasma level ≥ 2,000 and ≤ 150,000 copies/mL. Study Design: HIV-1 infected subjects, with a documented M184V variant, will be randomized to receive elvucitabine 10 mg QD or lamivudine 300 mg QD for 14 days. Subjects must be receiving a stable antiretroviral regimen (defined as no change in antiretroviral therapy for at least 4 weeks prior to randomization) that includes lamivudine or emtricitabine. At 72 hours prior to randomization, only lamivudine or emtricitabine will be stopped for washout; subjects will continue to receive the other drugs in their prescribed regimen (background antiretroviral therapy) during the 72-hour washout period. Subjects will then be randomized to receive blinded elvucitabine or lamivudine in a 1:1 ratio and continue to receive their prescribed background antiretroviral therapy for 14 days on an outpatient basis. Subjects will be followed for an additional 14 days post-treatment for safety, unless they enroll into the ACH443-018 extension study where they will continue to be treated and followed for safety.